To provide a structure of a tube member, which increases the strength against a bend, a torsion and the like by a slight enlargement of a cross section without an increase in weight, and to provide a method for manufacturing the tube member.

In the structure of a tube member, a projection 2 projecting outward in an axially perpendicular cross-sectional radial direction is formed in a corner 1 of an axis line deformation part in the tube member T having a square-shaped closed cross-section structure so as to increase a second moment of area of the tube member T, thereby increasing in stiffness against a bend and torsion.